In general, the invention relates to metabolic engineering of cells for the enhanced production of a cellular product.
Metabolic engineering involves the industrial production of chemicals from biological sources. Typically, a microbe such as a bacterium or a single-celled eukaryote is engineered to produce a compound in large amounts that is normally produced in small amounts or not at all. Examples of compounds produced by metabolic engineering include ethanol, butanol, lactic acid, various vitamins and amino acids, and artemisinin. Metabolic engineering generally involves genetic modification of a host organism, such as expression of foreign genes to make enzymes that synthesize compounds that may not be native to the host organism, overexpression of genes using strong promoters, introduction of mutations that alter allosteric regulation, and introduction of mutations that limit the production of alternative products.
It is generally desirable to produce compounds as cheaply and efficiently as possible. One major cost in metabolic engineering is the ‘feedstock’—the mixture of nutrients used in the medium in which the microbe grows. The feedstock typically includes a carbohydrate source, a source of fixed nitrogen, sources of sulfur, phosphorus, and so on, as well as any specific nutritional requirements. One significant problem in metabolic engineering is that even under conditions of product production, much of the feedstock is channeled into other metabolic pathways that contribute to growth of the organism and production of its biomass. A second problem is the cost of the feedstock itself, especially when the feedstock includes, in addition to a carbohydrate, molecules that fulfill auxotrophic requirements. Therefore, there is a need in the art to limit production of biomass during metabolic engineering and also to reduce the cost of the feedstock.